Abstract: PD40-08
Sources of Funding: none

Introduction

Multiparametric Magnetic Resonance Imaging (mp-MRI) and the 4Kscore blood test (OPKO: Miami FL) have both been shown to identify significant prostate cancer in men with elevated PSA. In comparison to a blood test, mp-MRI is resource intensive, thus is difficult to apply at a population level. Moreover, results from the PROMIS MRI trial show that 11% of men with normal MRI harbor high-grade disease. One possibility is selective application of mp-MRI to men at intermediate risk as defined by the 4Kscore: this would reduce the number of MRIs and lower the chance of missed high-grade disease. The aim of this study was to evaluate mp-MRI as a follow-up test to the 4Kscore in prostate cancer early detection.

Methods

The 4Kscore results from the US prospective validation study were combined with mp-MRI data available from the PROMIS study. Using the likelihood ratios for MRI detecting high grade disease and applying them to probabilities of 4Kscores, four different populations were identified based on a threshold for biopsy of 7.5% risk of high grade disease: 1. men with very low 4Kscore for whom risk would not be ≥7.5% even with positive MRI; 2. men with 4Kscores < 7.5% whose risk would be ≥7.5% if MRI were positive; 3. men with 4Kscores ≥7.5% whose risk would be <7.5% if MRI were negative; 4. men with high 4Kscores whose risk would remain ≥7.5% even if MRI were negative. In this strategy, group 1 would not be biopsied; groups 2 and 3 would receive MRI and then biopsy if MRI was positive; group 4 would be biopsied without MRI. Net benefit was calculated for each strategy using a threshold of 7.5%.

Results

In the 4Kscore validation study, 1012 men underwent prostate biopsy with 231 (23%) diagnosed with ≥Gleason 7 disease. PROMIS gave a positive and negative likelihood ratio of 1.58 and 0.17 for MRI. The range of 4Kscores that could be influenced by the results of MRI was 5-32%, i.e. group 1: 26% of the population with risk <5%; group 2: 10% with risk 5-7.4%; group 3: 45% with risk 7.5-32%; group 4: 21% with risk > 32%. Net benefit of using 4Kscores alone was 17.7%, mp-MRI 17.6%, and combined strategy 18.2%. A difference of 0.5% between the combined strategy and 4Kscore alone is equivalent to 62 fewer biopsies per 1000 for the same number of high grade cancers detected or about 9 MRI per biopsy avoided. Results were similar using a 10% threshold.

Conclusions

Using mp-MRI in the setting of low-intermediate 4Kscores results in a biopsy strategy with higher net benefit compared to using either modality alone. The proposed risk stratification minimizes the utilization of resources and reduces the excessive rate of missed high-grade disease associated with use of mp-MRI.

Funding

none